Re: [PATCH v3 6/8] KVM-HV: Add flush_on_enter before guest enter

[Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>]

On Thu, 2 Aug 2012 17:16:41 -0300, Marcelo Tosatti <mtosatti@redhat.com> wrote:
> On Thu, Aug 02, 2012 at 05:14:02PM -0300, Marcelo Tosatti wrote:
> > On Tue, Jul 31, 2012 at 04:19:02PM +0530, Nikunj A. Dadhania wrote:
> > > From: Nikunj A. Dadhania <nikunj@linux.vnet.ibm.com>
> > >  
> > >  static void kvm_set_vcpu_state(struct kvm_vcpu *vcpu)
> > >  {
> > > @@ -1584,7 +1573,8 @@ static void kvm_set_vcpu_state(struct kvm_vcpu *vcpu)
> > >  	kaddr = kmap_atomic(vcpu->arch.v_state.vs_page);
> > >  	kaddr += vcpu->arch.v_state.vs_offset;
> > >  	vs = kaddr;
> > > -	kvm_set_atomic(&vs->state, 0, 1 << KVM_VCPU_STATE_IN_GUEST_MODE);
> > > +	if (xchg(&vs->state, VS_IN_GUEST) == VS_SHOULD_FLUSH)
> > > +		kvm_x86_ops->tlb_flush(vcpu);
> > >  	kunmap_atomic(kaddr);
> > >  }
> > >  
> > > @@ -1600,7 +1590,8 @@ static void kvm_clear_vcpu_state(struct kvm_vcpu *vcpu)
> > >  	kaddr = kmap_atomic(vcpu->arch.v_state.vs_page);
> > >  	kaddr += vcpu->arch.v_state.vs_offset;
> > >  	vs = kaddr;
> > > -	kvm_set_atomic(&vs->state, 1 << KVM_VCPU_STATE_IN_GUEST_MODE, 0);
> > > +	if (xchg(&vs->state, VS_NOT_IN_GUEST) == VS_SHOULD_FLUSH)
> > > +		kvm_x86_ops->tlb_flush(vcpu);
> > >  	kunmap_atomic(kaddr);
> > >  }
> > 
> > Nevermind the early comment (the other comments on that message are
> > valid).
I assume the above is related to kvm_set_atomic comment in the [3/8]

> 
> Ah, so the pseucode mentions flush-on-exit because we can be clearing 
> the flag on xchg. Setting KVM_REQ_TLB_FLUSH instead should be enough
> (please verify).
> 
Yes, that will work while exiting. 

In the vm_enter case, we need to do a kvm_x86_ops->tlb_flush(vcpu), as
we have already passed the phase of checking the request.

Nikunj